Electric trace tube bundles, also referred to as trace tubing, typically comprises one or more process tubes traced with a heating cable, a heat transfer foil wrap, non-hygroscopic glass fiber insulation, and a PVC jacket. Applications include analyzer, impulse and instrument lines, small diameter process lines, stack gas sampling lines, and utility lines. The heating cable may be of a self-regulating type. Typical applications of such tubing include analyzer lines, process lines, stack gas sampling lines, and utility lines.
More complex electric trace tube bundles are often used as umbilicals for monitoring and probe control in a continuous emission monitoring system. The bundles may include a heated core section and an outer unheated probe support section all contained within an outer jacket. The heated core may include one or more tubes, such as sample, calibration and/or spare tubes. The inner core is heated by a heating cable that preferably provides uniform and consistent heating of the process tube or tube of the inner core. The heating cable can replace the heat that is lost through the thermal insulation system.
The inner core may also include a temperature sensor device, such as a resistance temperature device (RTD) or thermocouple, to allow for uniform heat control under various ambient and process conditions. The inner core usually is surrounded by non-hygroscopic glass fiber insulation. The outer section of the bundle, which is located outside the heated and insulated core section, may include tubes that do not need to be heated, electrical wires and probe temperature sensor wires, such as thermocouple extension cables. The unheated tubes may be used, for example, as air and calibration lines. The tubes can be of various sizes and uniquely identified, such as by color coding. The heated core section and unheated outer section are all contained within a jacket made of, for example, FR-PVC, FR-TFE or urethane materials.
Some continuous emission monitoring systems, such as systems used to monitor gas or particulate matter concentration or emission rate of smokestacks, require long analyzer bundle lengths. FIG. 1 shows a prior art umbilical 10 extending between monitoring equipment 12 and a probe 14 disposed in a process stream 16 at the top of a stack 18. The length of the umbilical 10 may exceed the effective operating length of the heater cable utilized therein, in which case not only must a power source 20 be provided at the monitoring end of the umbilical, but also at one or more locations 22 along the length of the umbilical. That is, a junction box 24 would be provided on the stack 18 at each location 22 for connection of power to the umbilical by means of a branched circuit box 26. In the case of a smokestack, the installer heretofore had to scale the stack to access power leads at one or more intervals along the length of the umbilical, and then cut through the sheath, and connect power leads at connection locations spaced no greater than the effective operating length of a heater cable extending to that location. After the splice was completed, the installer would then enclose the junction within the branched circuit box to protect the connection from the environment. Such installation procedure was time-consuming, difficult, tedious, and prone to error given the adverse conditions under which the connection had to be made.